Communication system



Aug. 19, 1941. H R w 2,253,144

COMMUNICATION SYSTEM Filed May 25, 1940 lhventor Hubert R. Shaw,

' Attorney Patented Aug. 19, 1941 COMMUNICATION SYSTEM Hubert It. Shaw, Drexel Hill, Pa., assignor to General Electric Company, a corporation of New York Application May 23, 1940. Serial No. 336,756

6 Claims.

My invention relates to communication systems in which three or more stations are arranged for intercommunicationL It is an object of my invention to provide certain improvements in. communication systems whereby assurance of privacy of conversation between any two of the stations is obtained and at the same time a reduction in the number of line circuits employed is secured where the system involves a large number of stations.

In certain systems involving three or more intercommunicating stations having no central switching station, to secure privacy of communication between any two stations an individual line circuit is employed extending from each station to each of the other stations. An object of myinvention is to avoid :the use, in such systems employing no central switching statiom of such individual circuits and at the same time to secure assurance of privacy. I I

It is a more particular object of my invention. to provide, in a communication systemin which a communication circuit is associated with each station and extends to every other station, means for assuring privacy of communication between any two stations by preventing connection of any third station to the communication circuit through which they are conversing.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself. however, both as to its organization and methodof operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing. in which the single figure represents an intercommunication system embodying my invention.

Referring to the figure I have shown an intercommunication system including three stations A, B, and C. Station A includes a sound translating. apparatus ID for transmitting and receiving sound, a relay II, a selector switch I2, and a pair of voltage dropping resistors l3 shunted by a condenser l4. Station A also has associated with it a pair of control conductors l5, and a pair of communication conductors IS.

The apparatus I may comprise a transmitter and a separate receiver for interconversion of sound and electric waves, or it may convenient- The relay II is adapted, when its coil is eni a spring 22.

ergized from a pair of control conductors, to connect a corresponding pair of communication conductors to the pair of leads I! connected to the speaker in the apparatus In.

FIhe selector switch I! has three operating buttons, !8, l9 and 20, so constructed that when one is depressed all others are released, In'the normal or standby position for station A the button I8 is depressed and is locked in that position by a. slide-barZl biased to the right by The shaft of button 18 extends through a slot in the slide-bar 2| and has a projection 23 which engages the body of the slide-bar when it is pulled to the right by the spring 22. The buttons I9 and Zfi cooperate with the slide-bar 2| in a similar way, so that if either button 19 or 20 is depressed. the slidebar 2| is moved to the left to release the button l8 and thereafter by moving to the right looks down the depressed button. The buttons I8, 19 and 20 are biased upwardly by springs 2525 and 26, respectively. 1 I

The button l8 in its depressed or standby position makes connection from a source of voltage in the apparatus Ill through the resistors [3' to the control conductors l5 and at the same time makes connection from the leads i1 to the communication conductor l6.

Station B comprises apparatus which is identical with that of station A, as well as with that at all other stations. Sound translating apparatus 21 at station B, which is similar to apparatus l0, includes a source of-voltage. which is connected through a pair of resistors 28 to "a pair of control conductors 3i, when a button 29 of a selector switch 30 is in its depressed position. A" pair of leads 32 from the speaker in the apparatus 21 are connected by contacts operated by the switch button 29 to a pair of com-@ munication conductors 33. I H

Sound translating apparatus 34 at station C is identical with apparatus in and 2! at station A and B. A source of voltage in apparatus 54 is connected through a pair of resistors 35 and. contacts operated by a button 36 of a switch 31 to a pair of control conductors 38. The button 36 also connects a pair of leads 39 from the speaker in apparatus 34 to a pair of communication conducto-rs 40. The button 19 at station A and the button 4! at station B areadapted when depressed to connect stations .A or B respectively to the pairs of conductors 33. and 4B. The buttons 20 and 42 at stations A and C are likewise adapted to connectst'ations--A and C respectively to the pairs of conductors 3| and 33.

:of the relay and place station C A temsat any one point is The buttons 43 and 44 at stations B and C are adapted when depressed to connect stations B and C respectively to the pairs of conductors l5 and I6.

In operation, for example, if the operator at station B desires to communicate privately with station C he depresses button 4| which simul taneously releases the button 29. The button 45 connects the coil of relay 45 at station E to the control conductors 38. The button 36 is depressed, as is the corresponding button at every station during standby condition, and therefore voltage is present on the conductors 33. This Voltage is sufiicient to operate the relay 45, which therefore connects 'the communication conductors 32 of station B through the contacts.

of button 4| to the communication conductors 40, which are connectedto the communication conductors 39 at station C. Conversation may be carried on through that connection.

No other station may interrupt this communicationbecause the current drawn by. the coil of relay '45 produces a voltage drop across reor more stations, those which embody my invention become very much more economical as the 7 number of stations is increased. For example,

sistors so that the voltage on conductors 38 is just sufiicient to hold relay closed,and" is not suflicient to operate any otherrelay. Therefore, even though the operator at'sta'tion A depresses the button l9, the relay ll cannot be operated and station A cannot interfere with the conversation between stations B and C. Since from the control conductors 3| and voltage is removed therefrom.

When the conversation between stations B and with 30 stations it is necessary to provide .pairs of conductors for a system embodying my invention, while it is necessary to provide 225 pairs of conductors at some points in other systems. V

It is obvious that as many more stations as needed may be added to such a system as I have shown if a pair of control conductors and a pair of communication conductors be supplied for each additional station. There must. also be supplied at each station an additional button in the selector switch, sinceat each station there must be one standby button and onebutton for every other station on the system.

With the type of selector switches which I haveshown for convenience in the drawing, it is possible to depress two or more buttons at once, so that simultaneous communication may be had between 3 or more stations. For example, if station A desires to communicate with both stations B and C, he must depress both buttons l5] and 20 simultaneously. Assuming that the buttons 29 and 36 are depressed in standby po sition,. station A is connected to both stations 7 B. and C It is of course necessary that the C is finished, the operator at station E need only depress the button-29 to place his station in standby condition again. If he fails to depress the button 29 but leaves his station in communicating condition with station C, the operator at station C cancommunicate with any station other than station E merelylby depressing the ,proper button. For example, 'by depressing the button 44, the 'button 3.6 is releasedwhich disconnects stations B and C. The button 44 connects the coil of relay 46 to control conductors l5, which have enough voltage to close'the contacts tion with station A. i

For each station in the system it is-necessary toprovide one pair of communication conductors and one pair of control conductors which two pairs are. connectedto, everyother station" in the.

system. It is thus necessary at any point to provide not more than twice as many pairs of in communicaconductors asthereare stations in the systems In the usual system it is necessary inorder to have private communication to provide onepair 'j of conductors-between each pair: of stations in the system. ,In a system using my invention therefore it is necessary to have 2% pairs of conductors, while. in usual systems it is necessaryto have I while? with my system the maximum number of pairs is 2n at any point. For systems having 10v pressed at a time.

used as station selector switches in' household voltage supplied through the resistors I3, 28 and 35 be properly poled for interconnection.

Since the mode of operation where two or more buttons 'may'bel depressed simultaneously introduces a slight possibility that some station may interrupt an existing communication'by' depressing one button corresponding to a communicating station and another button corresponding 'to a station in'standby condition, I find it of ad-- vantage in certain cases to provide selector switches in which only one'buttonmay be de- Such switches are comrnonly radio receivers. 7 It is, of course, within the scope of my invention to use any type of selector switch for performing the functions explained above.

While .I have shown a particular embodiment of my invention, it will, of course, be understood zthat I.-do not wish to be limited thereto, since different modificationsmaybe made both in the circuit arrangement and instrumentalities employed and I aim by. the'appended claimsto cover any such; modifications asfall "within the true spiritand scope of my invention; 7 What I' claim as new and desire to secure by Letters Patent of the UnitedStatesis:

1. In an intercommunication systemincluding at leastthree stations, apai-r of line circuits ex-' tending between said stations, means'ior connecting one of said stations normally to one of said line circuits, the other stations bei-ng'normally-disconnectedirom said one line-circuit, means to apply voltage of greater than a, pre

determined value to the other of saidfline 'cir-, cuits, meansin each other station responsive'to voltage on said other line circuit above said pre:

determined value to connect said other station to said one line circuit, and means to reduce said voltage on said other line circuit after opera tion of said voltage responsive means to a value below said predetermined value, whereby the cor,- responding voltage responsive means of 'a third station is thereafter unresponsive to'voltage on said other line circuit to connect said third sta' tion to said one line circuit 2. In an intercommunication systemincluding:

tending between said stations, means for connecting one of said stations normally to one of said line circuits, the other stations being normally disconnected from said one line circuit, means to supply voltage of greater than a predetermined value to the other of said line circuits, a relay in each other station arranged when energized to connect said other station to said one line circuit, means at said other station to energize said relay at the respective station from said other line circuit, said relay being operative only in response to voltage greater than said predetermined value and maintaining said other station connected to said one line circuit in the presence of voltage of a lesser value, and means efiective upon operation of said relay to reduce the voltage on said other line circuit to said lesser value, whereby the corresponding relay at a third station is thereafter unresponsive to voltage on said other line circuit to connect said third station to said one line circuit.

3. In an intercommunication system including three or more stations, a pair of line circuits extending between said stations, an impedance, means for connecting one of said stations normally to one of said line circuits, the other stations being normally disconnected from said one line circuit, means to supply voltage of greater than a predetermined value through said impedance to the other of said line circuits, a relay in each other station arranged when energized to connect said station to said one line circuit, and means at said other station to energize said relay from said other line circuit, said relay being operative only in response to voltage greater than said predetermined value and maintaining said other station connected to said one line circuit in the presence of voltage of a lesser value, said impedance being effective upon operation of said relay to reduce the voltage in said other line circuit to said lesser value by the voltage drop resulting from current through said impedance, whereby the corresponding relay at a third station is thereafter unresponsive to voltage on said other line circuit to connect said third station to said one line circuit.

4. In combination, at least three intercommunicating stations, a communication circuit and a control circuit corresponding to each station and extending between said stations, means to connect each station to its communication circuit and to supply voltage to said control circuits, means in each station to connect said station to the communication circuit of any desired station, said means in each station including means responsive to voltage on the control circuit of said desired station to effect said connection, and

means to reduce the voltage on the control circuit of said desired station after said voltage responsive means has effected said connection to a value sufficiently low that the voltage responsive means of any third station will not respond to said voltage to effect connection of said third station to the communication circuit of said desired station, whereby said third station is prevented from intercepting communication between two intercommunicating stations.

5. In combination, at least three intercommunicating stations, a communication circuit and a control circuit corresponding to each station and extending between said stations, means in each station to connect it to its communication circuit and to apply voltage to its control circuit or alternatively to connect it to the communication circuit of any desired station, said means in each station including means responsive to voltage on the control circuit of said desired station to effect said last connection, and means to reduce the voltage on the control circuit of said desired station after said voltage responsive means has effected said connection to a value sufliciently low that the voltage responsive means of any third station will not respond to said voltage to effect connection of said third station to the communication circuit of said desired station, whereby said third station is prevented from breaking in on communication between two already intercommunicating stations.

6. In combination, at least three intercommunicating stations, a communication circuit and a control circuit corresponding to each station and extending between said stations, means in each station to connect it to its communication circuit and to supply voltag to its control circuit or alternatively to connect it to the communication circuit of a desired station, said means including an electromagnetic relay operated by voltage on the control circuit of said desired station to effect said last connection, said relay comprising an operating coil and a switch operated thereby, said coil being adapted to close said switch only upon energization by voltage substantially higher than the voltage necessary to maintain it closed, and means to reduce the voltage on the control circuit of said desired station after said relay has efiected said connection to a value lower than said higher voltage so that the relay of any third station will not respond to said voltage to eiTect connection of said third station to the communication circuit of said desired station, whereby said third station is prevented from intercepting communication between two intercommunicating stations.

I-IUBERT R. SHAW. 

